The present invention relates to electronic musical instruments in general, and more particularly to improvements in circuits which generate and process tone signals in electronic pianos, electronic organs and like key-operated electronic musical instruments. Still more particularly, the invention relates to improvements in electronic musical instruments of the type wherein the volume of the tone is dependent on the magnitude of force with which the player strikes the keys of the keyboard or keyboards and wherein switching elements modulate the amplitude of tone signals in dependency on the characteristics of envelope voltage control signals which are generated in response to depression of keys.
In a known circuit of the above outlined character (such circuit is used in the so-called Effekt-Piano manufactured and sold since 1974 by the West German firm WERSI), the switching elements are gate circuits in the form of diodes. Owing to the threshold voltage of a diode, the envelope control voltage must exceed a value of 0.5-0.7 volt before the tone signal is transmitted to the signal processing stage or stages of the musical instrument. The same applies when the gate circuit is a conventional transistor because the base-emitter circuit of the transistor also exhibits such a threshold voltage. In view of the fact that the amplitude of tone signals in an electronic musical instrument is limited to approximately 10 volts, a linear relationship between the envelope control voltage and the modulated tone signal exists only to a minimum value of approximately 1 volt. This corresponds to a dynamic volume range of 10:1 or 20 decibels. However, the dynamic volume range of a mechanical piano or a concert piano is much wider, namely, between 40 and 60 decibels, which corresponds to volume differences of 100:1 to 1000:1.